The [SiCl6]2- ion is not known to exist or is highly unstable. This is primarily due to steric hindrance; six large chloride ions cannot be easily accommodated around a relatively small silicon atom. Additionally, the interaction between the lone pairs of the chloride ions and the vacant 3d orbitals of silicon is weak. On the other hand, [SiF6]2- is stable because fluorine atoms are much smaller and highly electronegative.